EV Charging Speed Explained: Why Your 11 kW Charger Doesn't Always Deliver 11 kW

You bought an 11 kW portable charger. You plugged it into your 11 kW-capable CEE socket. Your car supposedly has an 11 kW onboard charger. So why does your charging app show only 6 kW? Or 9 kW? Or sometimes the full 11 kW, but only for part of the session?

If this sounds familiar, you're not alone. EV charging speed is one of the most misunderstood aspects of electric vehicle ownership. The numbers on the spec sheet rarely match what you see in real life, and there are good reasons for that.

In this guide, we'll demystify EV charging speed. You'll learn why charging power fluctuates, what actually determines how fast your car charges, and how to calculate realistic charging times. No more guessing, no more frustration.

First Things First: kW vs kWh

Before we dive into charging speeds, let's clear up the most common confusion in the EV world: the difference between kW and kWh.

kW (Kilowatt) = Power

Kilowatt measures power , which is the rate at which energy flows. Think of it like the speed of water flowing through a hose. A 11 kW charger can deliver energy at a rate of 11 kilowatts.

When we say "charging at 11 kW," we mean your car is receiving 11 kilowatts of power at that moment. Higher kW = faster charging.

kWh (Kilowatt-hour) = Energy

Kilowatt-hour measures energy , which is the total amount of electricity stored or consumed. Think of it like the volume of water that fills a bucket. A 60 kWh battery can store 60 kilowatt-hours of energy.

When we say "my car has a 60 kWh battery," we mean it can store 60 kilowatt-hours of energy when fully charged.

The Simple Relationship

Here's the formula that connects them:

Energy (kWh) = Power (kW) x Time (hours)

Or rearranged to find charging time:

Time (hours) = Energy (kWh) / Power (kW)

Example:

If you need to add 44 kWh to your battery (say, from 20% to 100% on a 55 kWh battery) and you're charging at 11 kW, the calculation is: 44 kWh / 11 kW = 4 hours.

The Charging Chain: Where Bottlenecks Happen

Your actual charging speed is determined by the weakest link in a chain of components. Each link has a maximum power capacity, and you'll always charge at the speed of the slowest one.

Link 1: Your Electrical Installation

Everything starts at your home's electrical system. The power available depends on your socket type:

If you plug an 11 kW charger into a Schuko outlet, you'll only get 3.7 kW. The socket is the bottleneck.

Link 2: Your Portable Charger (EVSE)

Your portable charger (technically called EVSE, Electric Vehicle Supply Equipment) has its own power rating. Our Q11 and P11 chargers deliver up to 11 kW. The Q74 delivers up to 7.4 kW. The Q37, P35, and B35 deliver up to 3.7 kW.

If you have a CEE 32A Red socket (22 kW capable) but use an 11 kW charger, you'll charge at 11 kW maximum. The charger becomes the bottleneck.

Link 3: Your Car's Onboard Charger (The Most Common Bottleneck)

This is where most people get confused. Your EV has a built-in component called the onboard charger (OBC). Despite the name, it's not a charger in the traditional sense. It's a converter that transforms AC power from the grid into DC power that your battery can store.

The onboard charger has a fixed maximum power rating set by the manufacturer. This is almost always the limiting factor for home AC charging.

Common Onboard Charger Ratings:

Key insight: If your car has an 11 kW onboard charger, buying a 22 kW portable charger is a waste of money. Your car will still only charge at 11 kW because the onboard charger is the bottleneck. Match your charger to your car's capability.

Link 4: The Battery Itself

Even when all other components allow for maximum power, the battery itself may limit charging speed. This brings us to the factors that cause real-world charging to vary from the theoretical maximum.

Why Your Charging Speed Varies: The Real-World Factors

Even with perfectly matched equipment, you'll notice your charging power isn't constant. Sometimes it's lower than expected, sometimes it changes during a single session. Here's why.

Factor 1: Battery Temperature

Lithium-ion batteries have an optimal temperature range for charging, typically between 20°C and 40°C. Outside this range, your car's Battery Management System (BMS) will reduce charging power to protect the battery.

Cold battery (below 15°C):

• Charging power can drop by 20-50% or more
• The car may warm the battery before accepting full power
• This is especially noticeable in winter morning charging

Hot battery (above 40°C):

• Charging power is reduced to prevent overheating
• Common after highway driving in summer or repeated fast charging

Good news for home charging: AC charging generates much less heat than DC fast charging. With overnight charging at 11 kW, battery temperature is rarely a limiting factor except in extreme cold.

Factor 2: State of Charge (SoC)

Your battery's current charge level affects how fast it can accept more energy. This effect is much more pronounced with DC fast charging, but it exists for AC charging too.

Low SoC (0-20%): Some cars briefly limit power when the battery is very low, but most accept full AC power immediately.

Mid SoC (20-80%): This is the sweet spot. Most cars accept full AC charging power throughout this range.

High SoC (80-100%): Many cars reduce AC charging power above 80% to protect battery longevity. The last 20% often takes disproportionately longer. Some models reduce power above 90% or 95%.

Practical tip: For daily driving, charging to 80% is faster, gentler on the battery, and usually provides more than enough range. Save 100% charges for long trips.

Factor 3: Grid Voltage Fluctuations

Your home's electrical supply isn't always exactly 230V (or 400V for three-phase). Voltage can fluctuate between roughly 210V and 250V depending on grid load, time of day, and distance from the transformer.

Since Power = Voltage × Current, and current is limited by your circuit breaker, lower voltage means slightly lower power. You might see 10.5 kW instead of 11 kW during peak evening hours.

Factor 4: Single-Phase vs Three-Phase Balancing

Some EVs imported from markets with different electrical standards (particularly US-spec vehicles) can only charge on single-phase power, even when connected to a threee-phase supply. Instead of 11 kW (3 × 3.7 kW), they'll only draw 3.7 kW from one phase.

Check your car's specifications carefully. "11 kW capable" might mean "11 kW with three-phase power" but only "3.7 kW with single-phase."

How to Calculate Realistic Charging Time

Now that you understand the factors involved, let's put it all together with a practical calculation method.

The Basic Formula

Charging Time = Energy Needed (kWh) / Actual Charging Power (kW)

Step-by-Step Calculation

Step 1: Find your battery's usable capacity

Check your car's specifications. Note that advertised capacity (e.g., 77 kWh) is often gross capacity. Usable (net) capacity is typically 5-10% less due to buffer zones the car keeps for battery protection.

Step 2: Calculate energy needed

If your battery is at 20% and you want to charge to 80%, you need 60% of the usable capacity. For a 75 kWh usable battery: 75 × 0.60 = 45 kWh needed.

Step 3: Determine your actual charging power

This is the minimum of: your socket's capacity, your charger's rating, and your car's onboard charger. For most setups with Q11/P11 and a CEE 16A Red socket, this is 11 kW.

Step 4: Add efficiency losses (optional but realistic)

AC charging has about 85-90% efficiency. Some energy is lost as heat in the charger and onboard electronics. For a conservative estimate, multiply your enrgy needed by 1.1 to 1.15.

Step 5: Calculate

45 kWh × 1.1 (efficiency) = 49.5 kWh actual energy from the grid. 49.5 kWh / 11 kW = 4.5 hours

Quick Reference: Charging Times for Popular EVs

These times assume charging from 20% to 80% with an 11 kW charger (Q11 or P11):

Practical Tips for Maximizing Charging Speed

1. Match your charger to your car

Don't overspend on a 22 kW charger if your car only accepts 11 kW. You won't charge any faster, you'll just have paid more. Use our table above to find the right match.

2. Install the right socket

For most EV owners, a CEE 16A Red (three-phase) socket is the sweet spot. It provides 11 kW, which matches most cars' onboard chargers. Installation cost is reasonable, and you'll charge a typical EV from 20-80% in about 4 hours.

3. Charge overnight

At 11 kW, even a large 77 kWh battery charges from empty to full in about 7-8 hours. Plug in when you get home, wake up to a full battery. No need for faster charging at home.

4. Don't chase 100%

Charging slows down above 80%. For daily use, set your car's charge limit to 80%. You'll save time and extend battery life. Save 100% for long road trips.

5. In winter, charge immediately after driving

If possible, plug in while the battery is still warm from driving. You'll get faster charging than if you wait for the battery to cool down in freezing temperatures.

The Bottom Line

Your 11 kW charger not delivering 11 kW isn't a defect. It's physics. Your charging speed is determined by the weakest link in the chain: the power socket, the charger, the onboard charger, and the battery's current condition.

For home charging, the onboard charger is almost always the limiting factor. That's why matching your portable charger to your car's capability is so important. A Q11 or P11 (11 kW) is perfect for the vast majority of EVs. A Q22 (22 kW) only makes sense for the few cars with 22 kW onboard chargers.

The real magic of home charging isn't speed. It's convenience. You'll never visit a petrol station again. Every morning, your car is ready with exactly the charge you need. And at 11 kW overnight, you have more than enough power to keep up with even the heaviest daily driving.

Happy charging!

Find the Right Charger for Your EV:

Q11 (11 kW with WiFi): https://www.amperepoint.pl/products/portable-charger-q11-16a-11kw-type-2-display-bag-included-wifi

Q11 with Adapters: https://www.amperepoint.pl/products/portable-charger-q11-16a-11kw-type-2-display-bag-included-wifi-adapters

P11 (11 kW): https://www.amperepoint.pl/products/portable-charger-p11-16a-11kw-type-2

Q22 (22 kW with WiFi): https://www.amperepoint.pl/products/portable-charger-q22-32a-22kw-type-2-display-bag-included-wifi

Q74 (7.4 kW with WiFi): https://www.amperepoint.pl/products/portable-charger-q74-32a-7-4kw-type-2-display-bag-included-wifi

Sources:

(1) IEC 61851-1 - Electric vehicle conductive charging system

(2) SAE J1772 - Electric Vehicle and Plug-in Hybrid Electric Vehicle Conductive Charge Coupler

(3) Battery University - Charging Lithium-ion Batteries

(4) ADAC - Electric car charging test data

(5) European Automobile Manufacturers' Association - EV specifications database

(6) Manufacturer specifications: Tesla, Volkswagen, BMW, Skoda, Kia, Hyundai, BYD, Renault